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+"use strict";
+
+/**
+ * Attribution for work carried from another author's pull request.
+ *
+ * When a maintainer lands someone else's pull request by reimplementing,
+ * carrying, or rebasing it, the resulting commit is authored by the maintainer.
+ * The contributor survives only through a Co-authored-by trailer -- that trailer
+ * is what GitHub reads for the contributor graph, the repository's contributor
+ * list, and the author's own profile activity.
+ *
+ * This exists because the repository did it both ways for months. 53c09a247
+ * says "Clean reimplementation of #3193" and names alan7629 in a trailer;
+ * 5734a1caf says "Reimplements #2797 by @rrmlima" and names nobody. Both
+ * sentences are equally sincere, and only the first is data. A scan of dev
+ * found 27 landings whose author is named in prose and nowhere a tool can read;
+ * CREDITS.md is the record of those, and this check is why the list should not
+ * grow.
+ *
+ * The check reads the pull request's own text, not its diff, because that is
+ * where a carry declares itself.
+ */
+
+const CARRY_VERB_RE =
+  /\b(?:re-?implement(?:s|ed|ing|ation of)?|supersed(?:e|es|ed|ing)|carry(?: of)?|carries|carrying|carried(?: from)?|rebase(?: of)?|rebasing|adopts the design from)\b/gi;
+
+/**
+ * Every reference in one window, keeping any owner/repo qualifier.
+ *
+ * A bare "#2797" means this repository. "other/project#2797" does not, and
+ * resolving it here would look up an unrelated pull request of the same number
+ * in this one -- comparing the trailer against the wrong person. Qualified
+ * references are captured so they can be dropped rather than misread.
+ */
+const REF_RE = /(?:([\w.-]+\/[\w.-]+))?#(\d+)/g;
+
+/**
+ * The window a carry verb governs: to the end of its sentence, capped at 80
+ * characters. Both bounds are load-bearing.
+ *
+ * The sentence bound is why "Supersedes #3193. Fixes #3192." reports only
+ * #3193 -- that is 53c09a247's real body, and a fixed-width window would have
+ * pulled the issue it closes into the carry set and demanded a trailer for the
+ * reporter. The width cap is why a verb cannot reach across a paragraph into an
+ * unrelated reference list.
+ */
+const SENTENCE_END_RE = /[.!?](?:\s|$)|\n/;
+
+function carryWindow(text, from) {
+  const slice = text.slice(from, from + 80);
+  const end = slice.search(SENTENCE_END_RE);
+  return end === -1 ? slice : slice.slice(0, end);
+}
+
+const TRAILER_RE = /^[ \t]*co-authored-by:[ \t]*(.+)$/gim;
+
+const FENCED_CODE_RE = /^[ \t]*(\u0060{3,}|~{3,})[\s\S]*?^[ \t]*\1[ \t]*$/gm;
+const INLINE_CODE_RE = /\u0060[^\u0060\n]*\u0060/g;
+const HTML_COMMENT_RE = /<!--[\s\S]*?-->/g;
+
+/**
+ * Carry language inside a fenced block, an inline span, or an HTML comment is
+ * quoted material, not a declaration. A pull request that explains the gate
+ * itself -- this one does -- must not trip it.
+ */
+function strippedText(text) {
+  if (typeof text !== "string") return "";
+  return text
+    .replace(FENCED_CODE_RE, "")
+    .replace(HTML_COMMENT_RE, "")
+    .replace(INLINE_CODE_RE, "");
+}
+
+function hasLabel(labels, name) {
+  return (labels || []).some(
+    (label) => (typeof label === "string" ? label : label?.name) === name,
+  );
+}
+
+/** Pull request numbers this text claims to carry, supersede, or rebase. */
+function referencedCarryNumbers(...texts) {
+  const found = new Set();
+  for (const text of texts) {
+    const stripped = strippedText(text);
+    CARRY_VERB_RE.lastIndex = 0;
+    let verb;
+    while ((verb = CARRY_VERB_RE.exec(stripped)) !== null) {
+      const window = carryWindow(stripped, verb.index + verb[0].length);
+      REF_RE.lastIndex = 0;
+      let ref;
+      while ((ref = REF_RE.exec(window)) !== null) {
+        // A qualified reference names a pull request in another repository.
+        if (ref[1]) continue;
+        found.add(Number(ref[2]));
+      }
+    }
+  }
+  return found;
+}
+
+function trailerValues(...texts) {
+  const values = [];
+  for (const text of texts) {
+    if (typeof text !== "string") continue;
+    TRAILER_RE.lastIndex = 0;
+    let match;
+    while ((match = TRAILER_RE.exec(text)) !== null) values.push(match[1].toLowerCase());
+  }
+  return values;
+}
+
+/**
+ * A GitHub login is not a git identity. The scan behind CREDITS.md produced
+ * eleven false positives from that assumption alone: a login like "asmith92"
+ * does not appear anywhere in a trailer that reads "A. Smith <a@example.com>",
+ * even though they are the same person. Match on any of the three identifiers
+ * the referenced pull request actually carries.
+ */
+function parseTrailer(value) {
+  const match = /^\s*(.*?)\s*<([^>]*)>\s*$/.exec(value);
+  if (match) return { name: match[1].toLowerCase(), email: match[2].toLowerCase() };
+  return { name: value.trim().toLowerCase(), email: "" };
+}
+
+/**
+ * Substring matching is not good enough here, and the failure is not exotic:
+ * an author named "Ann" would be satisfied by "Co-authored-by: Joanne
+ * <other@example.com>", and a short login can appear inside an unrelated
+ * address. A trailer credits someone only when its name or its email equals an
+ * identifier the referenced pull request actually carries.
+ */
+function trailerNames(author, trailers) {
+  if (!author) return true;
+  const names = new Set(
+    [author.login, ...(author.names || [])]
+      .filter((value) => typeof value === "string" && value.trim() !== "")
+      .map((value) => value.trim().toLowerCase()),
+  );
+  const emails = new Set(
+    (author.emails || [])
+      .filter((value) => typeof value === "string" && value.trim() !== "")
+      .map((value) => value.trim().toLowerCase()),
+  );
+  if (names.size === 0 && emails.size === 0) return true;
+  return trailers.some(
+    (trailer) =>
+      (trailer.name !== "" && names.has(trailer.name)) ||
+      (trailer.email !== "" && emails.has(trailer.email)) ||
+      // A GitHub noreply address carries the login after the numeric id,
+      // before the "@" -- that is the only identifier many trailers have.
+      (trailer.email.endsWith("@users.noreply.github.com") &&
+        names.has(trailer.email.replace(/^[^@]*?(\d+\+)?/, "").split("@")[0])),
+  );
+}
+
+/**
+ * @returns {{ code: string, paths: string[] }[]} empty when the pull request may proceed
+ */
+function assessCarryAttribution({
+  prAuthorLogin = "",
+  title = "",
+  body = "",
+  commits = [],
+  labels = [],
+  referencedAuthors = {},
+} = {}) {
+  if (hasLabel(labels, "attribution-approved")) return [];
+
+  const referenced = referencedCarryNumbers(title, body, ...commits);
+  if (referenced.size === 0) return [];
+
+  // The squash body is assembled from the pull request body and the branch's
+  // commit messages, so both are where an author can put the trailer today.
+  const trailers = trailerValues(body, ...commits).map(parseTrailer);
+  const uncredited = [];
+
+  for (const number of referenced) {
+    const author = referencedAuthors[number];
+    // An unresolved author is a pass. A rate limit or a deleted account must
+    // never be the reason a merge is blocked.
+    if (!author) continue;
+    // Referencing your own earlier branch is ordinary maintenance.
+    if (
+      author.login &&
+      prAuthorLogin &&
+      author.login.toLowerCase() === prAuthorLogin.toLowerCase()
+    ) {
+      continue;
+    }
+    if (!trailerNames(author, trailers)) uncredited.push("#" + number);
+  }
+
+  if (uncredited.length === 0) return [];
+  return [
+    {
+      code: "missing_coauthor_credit",
+      paths: uncredited.sort(),
+    },
+  ];
+}
+
+module.exports = {
+  CARRY_VERB_RE,
+  carryWindow,
+  assessCarryAttribution,
+  referencedCarryNumbers,
+  strippedText,
+  trailerValues,
+};